1. Field of the Invention
The present invention pertains to network design and determining arrangement of optical transmission devices in respective stations.
2. Description of the Related Art
In recent years, with use of optical add drop multiplexers (OADM) in optical networks, data in a channel is extracted from or added to a wavelength division multiplexed (WDM) optical signal.
OADMs are mainly used at the beginning or termination point of traffic but can be provided at a relay station to be used as repeaters that regenerate an arbitrary block of traffic. When a WDM network is designed, information concerning a station that can house a WDM transmission device, information concerning an optical mesh network built with optical fibers, and information concerning traffic are generally provided as input information (see Japanese Patent Application Laid-Open Publication Nos. 2006-135788 and 2006-42279).
A station at the beginning or termination point of traffic is equipped with an OADM. Other stations (relay stations) can be equipped with a WDM transmitting device such as an OADM functioning as a repeater or an in-line amplifier (ILA), and it is necessary to determine which device is to be provided. A rely station may be without a WDM transmitting device to simply connect optical fibers (bypass station).
In a mesh WDM network, especially at a linear section between each OADM station at the beginning or termination point of traffic or between optical hub stations having three or more connections, various configurations can be considered which have, for example, different device costs, optical signal noise ratios (OSNR), and optical path penalties (degradation), depending on the combination of WDM transmission devices provided in the relay stations in the linear section.
When a WDM network is designed, a WDM transmission device arrangement that minimizes cost and takes traffic distribution into consideration is preferable for each linear section. Conventionally, all possible combinations of device placement for each linear section are evaluated to compute a comprehensive cost including various parameters such as equipment cost or optical signal degradations so that a combination of device placements having the least cost is selected.
However, according to the conventional techniques, since all possible combinations of device placement in stations are evaluated to compute cost with various parameters, the number of combinations and computed costs becomes enormous as selectable devices or stations increase, whereby the processing time increases. Further, when design is conducted based only on comprehensive cost, although comprehensive cost may be reduced, optical signal degradation can exceed the range within which light can be regenerated by an optical regenerative repeater.
In traffic, each optical transmission parameter has a threshold and when the optical transmission parameters degrade below the threshold, light cannot be regenerated by the optical regenerative repeater. Therefore, in a section where optical transmission parameters degrade beyond the threshold, a device functioning as the optical regenerative repeater must be provided; otherwise transmission is not possible as the degradation of the optical signal exceeds the threshold.